While officials have identified the area responsible for the romaine lettuce E. coli outbreak reported days before Thanksgiving, people should still pause before ordering a salad or buying lettuce at the grocery store.

At least 52 people in 15 states have become sick after eating contaminated romaine lettuce, the CDC reported Thursday. Illnesses started between Oct. 5 and Nov. 18. At least two have people have suffered kidney failure.

Here’s what we know about the outbreak:

What do we know about the contaminated lettuce?

Last month, the Food and Drug Administration announced that the contaminated lettuce likely came from crops in California, specifically Central Coast growing regions of northern and central California, based on “growing and harvesting patterns.” Still, the CDC has identified no common grower, supplier, distributor or brand.

Yes. The CDC is still asking people not to eat the lettuce and retailers to avoid selling it, unless they are positive it didn’t come from the affected area. They are still investigating the exact cause of the outbreak.

Is romaine lettuce back on grocery shelves?

Yes. Retailers are stocking shelves with romaine lettuce again. Consumers are still advised to double-check labels before purchasing.

Romaine lettuce that was harvested outside of Central Coast growing regions of northern and central California is safe to eat. The problem is that not all lettuce labels show where it’s harvested. So, if you’re unsure, throw it out or don’t buy it. Hydroponically- and greenhouse-grown romaine lettuce is also safe to eat.

What do I do if I think I have an E. coli infection?

If you have symptoms of E. coli infection, such as stomach cramps, bloody diarrhea and vomiting, talk to your doctor and report the illness to the health department.